272 KNUDSON : CAMBIUM DEVELOPMEMT IN AMERICAN LARCH 



activity began from two to four weeks later in the lower part of 

 the trunk than in the twigs. 



As a result of extensive investigations, Robt. Hartig* advanced 

 the idea that cambial awakening was dependent upon temperature 

 and that therefore the thickness of the bark, temperature of the 

 soil moisture, and insolation, were important factors. He found 

 in an isolated lo-year old Pinus sylvestris, that cambial activity 

 had begun two weeks earlier than in isolated 35- and 65-year old 

 trees, and four weeks earlier than in a loo-year old tree grown 

 under forest conditions. The comparisons were all made at a 

 height of 6 meters. He also found that under natural forest 

 conditions the growth of the annular ring of Scotch pine, Norway 

 spruce, and European larch at a height of 27.5 meters, was on 

 June 9 respectively 66 per cent, 56 per cent and 75 per cent 

 completed. Going toward the base the growth decreased, and 

 at a height of 1.5 meters the percentage of the annular ring com- 

 pleted was 35, 21 and 18 per cent respectively. In isolated trees 

 of Scotch pine and Norway spruce the growth on July 9 was ap- 

 proximately the same in all parts of the trunk. Under forest 

 conditions growth was found to begin in the twigs and proceed 

 downward, the cessation of growth following the same order. 



According to Mer,f the cambial activity in oak, beech, bass- 

 wood, fir, and other trees of twenty-five years of age and under 

 begins in the youngest twigs. In older trees cambial activity 

 Is described as simultaneous at the bases of the branches and 

 trunk. He states also that in a single cross-section cambial 

 activity may be evident on one side and not on another. 



Hastings! found that in broad-leaved trees increase in cliam- 

 eter did not begin until the buds had opened. He found that 

 growth first begins in the, I -year old twigs, and later it occurs in 

 2- and 3-year old twigs. When wood is forming in 5- or 6-year 

 old growth there is simultaneous development over the entire 

 tree. In pine it begins first in the 2- and 3-year old twigs. In 

 the hemlock the growth was first observed in the 6-year old twigs, 



* Hartig, R. Das Holz der deutschen Nadelwaldbaume, 35~38. 1885. 



t Mer, E. Sur les causes de variation de la densite des bois. Bull. Soc. Bot. 

 France 39: 95-io5- 1892. 



t Hastings, G. When increase in thickness begins in our trees. Science II. 

 12:585. 1900. 



